An impedance-to-voltage converter utilizes an operational amplifier to convert an impedance into a voltage without suffering from the influence of stray capacitances. The impedance-to-voltage converter is formed of an operational amplifier which has an imaginary short-circuit state between an inverting input and a non-inverting input thereof when an impedance element is connected between an output and the inverting input, a shielding line for shielding a line for connecting the impedance element to the inverting input, an AC signal generator connected to the non-inverting input, and a shielding line for shielding the signal line. The shielding lines are connected to the non-inverting input.